I have a 25 cal semi-automatic Colt pistol. The serial# is 403xxx. It is nickel plated with standard Colt grips. Here is my question: Just forward of the trigger on the trigger gard is the number 55 on the right side. On the left side in the same area is the letter P and a triangle with what appears to be a letter P with some slashes inside it. The triangle is below the letter P. Does anyone know what these markings signify? Thank you,in advance.